1. Field of the Invention
The present invention relates to a thermal convection-type accelerometer, and relates more particularly to a thermal convection-type accelerometer whose heater and temperature-sensing components are not suspended.
2. Description of the Related Art
U.S. Pat. No. 6,182,509 discloses a thermal convection-type accelerometer, which comprises a silicon substrate, a heater and two temperature sensors. The silicon substrate has a deep cavity formed underneath the heater and the temperature sensors. The temperature sensors are positioned at equal distances from the heater on either side thereof.
In order to form a cavity underneath the heater and the two temperature sensors, a silicon dioxide layer is initially formed on the silicon substrate. Thereafter, a poly-silicon layer is formed on the silicon dioxide layer. Next, an oxide layer is formed on the poly-silicon layer using an oxidation process. Subsequently, the poly-silicon layer is patterned to form three poly-silicon bridges. Then, an oxidation process is performed to form an oxide layer on the sides of the poly-silicon bridges. Next, EDP (a mixture of ethylenediamine, pyrocatechol and water) is applied to etch a deep cavity.
According to the description of the above process, the process for manufacturing suspended heaters and temperature sensors is complex and results in thermal convection-type accelerometers being quite expensive. Furthermore, the slender poly-silicon bridges are easily damaged during the manufacturing of the thermal convection-type accelerometer, resulting in a low yield ratio and are easily broken when the thermal convection-type accelerometer operates for a long period of time. Moreover, the components of the above thermal convection-type accelerometer are formed on a silicon substrate. Because the silicon thermal conductivity (1.48 W/(m−K)) is larger, it can quickly dissipate the heat generated from the heater. Therefore, the heater must be formed over a cavity to reduce energy loss. However, despite forming a deep cavity underneath the heater, the silicon substrate still dissipates a significant amount of heat. As a result, thermal convection-type accelerometers using silicon as their substrates will consume larger amounts of energy. In addition, the cavities of present thermal convection-type accelerometers are filled with carbon dioxide or specified concentrations of air, and the gases may oxidize the heaters and temperature sensors, causing the thermal convection-type accelerometers to have a shorter lifespan.
As noted, conventional thermal convection-type accelerometers have some drawbacks. Therefore, a new thermal convection-type accelerometer is required.